1. Technical Field
The present disclosure relates to a system and a method for controlling engine clutch delivery torque of a hybrid electric vehicle. More particularly, the present disclosure relates to a system and a method which maintains engine speed of a predetermined speed, such as an idle speed, and controls operation of an integrated starter-generator so that the integrated starter-generator may generate the engine clutch delivery torque according to hydraulic pressure of the engine clutch when an engine clutch delivery torque is learned, so that engine booming does not occur and noise, vibration, and harshness (NVH) is reduced.
2. Background
Hybrid electric vehicles operate through the use of power from an internal combustion engine and power from a battery. In particular, hybrid electric vehicles are designed to efficiently combine and use power of the internal combustion engine and the motor.
For example, as illustrated in FIG. 1, a hybrid electric vehicle includes an engine 10, a motor 20, an engine clutch 30, a transmission 40, a differential gear unit 50, a battery 60, an integrated starter-generator (ISG) 70, and wheels 80. The engine clutch 30 controls power between the engine 10 and the motor 20, and the ISG 70 starts the engine 10 or generates electric power by output of the engine 10.
As further shown, the hybrid electric vehicle includes a hybrid control unit (HCU) 200 which controls overall operation of the hybrid electric vehicle; an engine control unit (ECU) which controls operation of the engine 10; a motor control unit (MCU) 120 which controls operation of the motor 20; a transmission control unit (TCU) 140 which controls operation of the transmission 40; and a battery control unit (BCU) 160 which manages and controls the battery 60.
The battery control unit 160 may also be referred to as a battery management system (BMS). In the vehicle industry, the ISG 70 may also be referred to as a starting/generating motor or a hybrid starter & generator.
The hybrid electric vehicle may run in a driving mode, such as an electric vehicle (EV) mode using only power of the motor 20, a hybrid electric vehicle (HEV) mode using torque of the engine 10 as main power and torque of the motor 20 as auxiliary power, and a regenerative braking (RB) mode during braking or when the vehicle runs by inertia. In the RB mode, braking and inertia energy are collected through power generation of the motor 20, and the battery 60 is charged with the collected energy.
In particular, the hybrid electric vehicle may run in one mode among the HEV mode, EV mode, and RB mode, by engaging or disengaging the engine clutch according to the intention of the driver operating the accelerator pedal and the brake pedal, the load, the vehicle speed, the state of charge (SOC) of the battery, and so on.
It is possible to ensure drivability of the hybrid electric vehicle by engaging the engine clutch after the engine speed and the motor speed are synchronized to maintain a constant torque during power transmission between the engine and the motor, when changing from the EV mode to the HEV mode. In order to do so, it is helpful to precisely control the engine clutch.
The delivery torque of the engine clutch, which is torque, or load at both ends of the engine clutch, transmitted by physical contact between the friction surfaces of both ends of the engine clutch, can be estimated from the efficient pressure and the friction coefficient.
Controlling the engine clutch is a very important factor that determines the drivability and the fuel consumption in starting the hybrid electric vehicle. However, the friction coefficient changes with a deviation in current and pressure characteristics of a solenoid valve operating the engine clutch, aging of the solenoid valve, and degradation of the friction members at both ends of the engine clutch, which may generate characteristic deviations.
As described above, it is difficult to precisely control the engine clutch, because characteristic deviations of the engine clutch are generated, thereby decreasing drivability and fuel consumption. Therefore, it would be beneficial if the characteristic deviation of the engine clutch is compensated or corrected through learning of an engine clutch delivery torque.
A conventional method of learning engine clutch delivery torque is performed mostly in a low hydraulic pressure region of an engine clutch to prevent a booming operation which may occur in low speed and high torque operation region of an engine, but is not performed in a high hydraulic pressure region of an engine clutch.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure.